The present invention relates to a disposable absorbent articles such as diapers, sanitary napkins, pantiliners, tampons, perspiration pads, adult incontinence devices and the like to be attached directly to the skin of the wearer. The articles utilise an improved adhesive so as to facilitate easy application and removal of the article from the wearer, whilst ensuring maintenance of the article in the desired position. In particular the adhesives provide attachment on moist and wet skin for the entire period of wear, including circumstances or periods of wear during which the adhesive is exposed to excess amounts of liquids.
The present invention relates to adhesives which are particularly useful to absorbent articles for absorption of body liquids which naturally emanate from a body without a wound. For example to attach sanitary napkins or pantiliners in the genital region. Also incontinence devices which are worn e.g. in the genital region or perspiration pads which are worn in the arm pit region of a person can suitably employ the adhesive of the present invention.
Such adhesives have been generally disclosed in for example U.S. statutory invention registration H1602 or WO 96/33683 and WO 95/16424. The latter discloses sanitary articles having a topical adhesive which is applied on the wearer facing side of a sanitary napkin along the entire periphery. WO 96/13238 discloses a topical adhesive which is described in terms of frequency dependency. EP-638 303 discloses the use of a topical adhesive on side cuffs of sanitary napkins in order to keep the cuffs in an upright position. Swiss publication CH-643730 discloses the use of a very long sanitary napkin having chamfered outer edges with a topical adhesive at the four corners of the outer edges in order to provide a topical adhesive area well outside the region of pubic hair growth.
However all of these disclosures typically disclose a product which is designed to be utilised in combination with an undergarment and hence the degree of adhesion actually provided is very low and is not designed to withstand any excessive pressure. Moreover the adhesive is only discussed in general terms or concentrates on the area of application of the adhesive to the article. The nature of adhesive per se other than the basic physical requirements such as pressure sensitivity are not discussed in particular with reference to the chemical composition or the adhesive criteria.
The prior art in the general field of adhesives for attachment to the skin is particularly developed in the field of articles such as band-aids, plasters and bandages. These articles are however typically applied in an emergency situation, where for example, a cut into the skin of the wearer has occurred and absorption of the body liquids emanating from a wound is desired. In this context performance aspects of the article such as easy application and use of the product, comfortable wear as well as painless removal, and discreteness are again subordinate, to other criteria in this case such as sterility, healing support, and mechanical protection of the wound. Also such wound covering absorbent articles are mostly adhered to the skin where prior to application of the absorbent article bodily hair can be removed or where little hair grows.
In order to provide the desired level of adhesion of such bandages, the prior art typically discloses the utilisation of certain adhesives having very high cohesive strengths such as rubber based adhesives and acrylics. These adhesives are then applied as thick layers to maximise the adhesive force by which the bandage is secured to the skin of the wearer.
U.S. Pat. No. 4,699,146 discloses hydrophilic elastomeric pressure sensitive adhesives suitable for use with ostomy devices, bandages, ulcer pads, sanitary napkins, diapers, and althetic padding. The adhesive comprises at least 1 uradiation cross linked organic polymer and an adhesive plasticizer.
GB 2 115 431 discloses adhesives for bandages, wounds or burn dressings, EKG adhesives, sanitary napkins, diapers and ulcer pads. The adhesive comprises an uradiation cross-linked organic polymer such as polyvinylpyrrolodine and an adhesive plasticizer.
However, for application such as absorbent articles it is important that the adhesive has a skin compatible composition and not be harsh or aggressive towards the skin or cause skin irritation or inflammation. Also it is preferred if the adhesive is compliant with the skin of the wearer such that maximum skin surface contact between the adhesive and the skin is achieved. Moreover, it is also desirable to provide an adhesive such that the absorbent article can be readily removed from the wearer, without the wearer experiencing any unacceptable pain level. This is particularly important under circumstances, where the article is removed and reapplication of the article once or even a number of times is required for example to allow for urination and or to ensure the application of such articles on sensitive skin and wearer groups such as infants. However, on the other hand the desired level of adhesion, albeit painless should of course also be maintained during such multiple applications of the article.
The problem of achieving the desired adhesion level is further exacerbated under wet skin conditions. Typically, prior to the placement of the article the skin is cleaned and is usually as a result moist. The currently available adhesives, such as hydrocolloids, however often do not immediately strongly adhere to the skin and may need to be held in place until sufficient minimum adhesion occurs. Moreover, the overall adhesive ability of such adhesives tends to be significantly reduced on wet skin surfaces per se, so that the article will typically not remain attached to the skin during wearer if any pressure is exerted onto the article, for example by the movement of the wearer.
Moist and wet skin however is not just a problem which is prevalent at the article application stage as a significant amount of moisture is also generated during the use of the article from the wearer by perspiration and from bodily fluids. Under such circumstances currently available adhesives typically cannot absorb this moisture and again the adhesive strength is reduced to such an extent that the article will often become detached under exertion of pressure during wear. It is hence very important to provide an adhesive which provides both initial adhesion and maintenance of its adhesive strength on wet skin. Moreover, it is also another important factor for the product performance that the adhesive is also stable to exposure to excess quantities of liquid such as water, urine and menstrual fluids and will also not loose its adhesive strength under such circumstances.
None of the prior art in the field of absorbent articles however even recognises or addresses the problem of providing these articles with an adhesive which meets these criteria, in particular adhesives which adhere to wet skin and are stable and maintain their adhesiveness even when exposed to excessive amounts of liquid.
Adhesion to wet skin is addressed for example in WO 98/03208 which discloses medical pressure sensitive adhesives which can adhere to dry or wet skin and which comprise a mixture of hydrophilic (meth)acrylate copolymer containing tertiaryamino groups, a hydrophilic (meth)acrylate copolymer containing carboxyl groups, carboxylic acids and a crosslinking system. However this document does not discuss adhesion after exposure to excess liquid.
Hence there still exists a need to disposable absorbent articles having an adhesive for the secure attachment and painless removal of the article from the skin suitable for use of sensitive skin of an infant and or of the genitalia and it is thus an object of the present invention to provide such an article.
It is another objective of the present invention to provide an adhesive that exhibits an ability to adhere to skin upon reapplication, particularly multiple reapplication for example when the article is removed for urination purposes or is misplaced, whilst still allowing painless removal.
It is yet a further objective of the present invention that the adhesive will adhere to moist or wet skin, independent of whether this is direct application of the article onto wet skin, or moisture which is generated on the skin surface during the wearing period of the article. In particular it is an objective of the present invention to provide an adhesive which is liquid stable particularly to water and urine, such that the adhesion properties will not be significantly effected in the presence thereof over the period of wear of the article.
It is another object of the present invention to provide an adhesive which upon removal from the skin of the wearer leaves no residues. It is yet another object of the present invention to provide an adhesive which does not cause a cold or otherwise unacceptable temperature sensation upon application to the wearer.
An additional object of the present invention to provide an adhesive which provides flexibility, stretchability and contractability so that it is able to adapt to the contours of the body during all bodily movements and hence be comfortable for the wearer of the article, whilst still having sufficient adhesive capacity to ensure secure attachment during use.
It has now been surprisingly found that the above drawbacks will be substantially alleviated by providing the absorbent article with an adhesive as defined hereinafter. The adhesive provides secure attachment, is pleasing to the skin upon application, and yet causes no discomfort upon removal and maintains its adhesive strength over the period of wear even under exposure to excess liquids.
Any disposable absorbent article known in the art can be provided with the adhesive according to the present invention. According to the present invention the adhesive is provided so as to have an initial peel strength (PI) under normal ambient conditions and a final peel strength (PF) after exposure to water according to the test method described herein, whereby the ratio of PI to PF is from 2:1 to 2:4 preferably from 2:1.25 to 2:2.5 and has a water absorption capacity as defined in the test herein of at least 3% by weight of said adhesive.
The adhesive allows attachment of disposal absorbent articles to the skin of the wearer, the adhesive being provided as a layer having a certain thickness or calliper C measured in millimeters (mm), typically on at least part of the wearer facing surface of the article.
Detailed analysis of the sequence of common situations occurring from the application of absorbent articles to the time of removal of such articles has shown that specific adhesive characteristics need to be preferably satisfied in order to achieve the desired performance objectives, in particular to secure initial attachment, secure attachment during use and painless removal after wear. The characteristics which have been considered in this context are the elastic modulus describing the elastic behaviour of the material and the viscous modulus which describes the viscous behaviour of the adhesive material.
The viscous behaviour of the adhesive can be interpreted to represent an indication of the ability of the adhesive to quickly attach and securely adhere to a particular surface. The elastic behaviour can be interpreted as an indication of the xe2x80x9chardnessxe2x80x9d behaviour of the adhesive. Its value is also important for good initial attachment. Their combination is believed to be an indicator of the required force upon removal. The relation between elastic and viscous modulus is considered to be an indication on which fraction of the removal energy will be dissipated within the adhesive and which fraction is available to trigger the actual removal.
In order to provide adhesives for secure initial and prolonged attachment and easy/painless removal the relation between the elastic modulus and the viscous modulus as well as their dynamic behaviour is also of importance.
The adhesive has an elastic modulus at a temperature of 37xc2x0 C. (100xc2x0 Fahrenheit) abbreviated Gxe2x80x237, a viscous modulus at a temperature of 37xc2x0 C. (100xc2x0 Fahrenheit) of Gxe2x80x337, and a viscous modulus at a temperature of 25xc2x0 C. (77xc2x0 Fahrenheit) of Gxe2x80x325.
The adhesive according to the present invention preferably satisfies the following conditions;
Provided the above rheological conditions are satisfied the adhesives will also satisfy conditions such as sufficient cohesiveness (to prevent residue of adhesive on the skin) which are important for commercial use of such adhesives and apparent to those skilled in the art. Adhesive compositions which satisfy the above criteria can be used as adhesives for the article provided they also satisfy the common requirements of being safe for use on human or animal skin during use and generally after disposal of the article.
Often the criteria of hygienic appearance such that adhesive compositions which are transparent or white upon application are preferred.
It has been determined that the relation between the thickness or calliper C, measured in millimeters (mm), of the layer in which the adhesive is provided, typically onto at least a portion of the wearer facing surface of the article, and the viscous modulus Gxe2x80x325 at about 100 rad/sec of the adhesive, is relevant to the scope of providing an easy and painless removal from the wearer""s skin of such a adhesive applied on at least a portion of the wearer facing surface of an absorbent article for attachment of said article to the skin of a wearer.
The adhesive of the present invention is thus preferably provided as a layer having a thickness C such that the viscous modulus Gxe2x80x325 (100 rad/sec) and the thickness C preferably satisfy the following empirical equation:
Gxe2x80x325xe2x89xa6[(7.00+C)xc3x973000] Pa
and preferably also the following empirical equation:
Gxe2x80x325xe2x89xa6[(5.50+C)xc3x971700] Pa